As a prospective teacher of English I have been looking at various schools and CELTA providers. They say that age is not a problem but increasingly I see many job ads with upper age limits.
I am now 59, I know I should be dead but the fact is I am not. I have a degree which I obtained only 5 years ago. I also have a business qualification which I would still like to put to use. Am I being unrealistic in thinking that I can work overseas teaching English?

I think that in the world of EFL it is very difficult to be specific. Everything depends on where you are looking for work. There are many factors to consider including the country where you want to work, the school, the type of teaching you want to do (children, businessmen etc etc). Some schools may have a preference for younger teachers and others for people like yourself who have real and extended work experience. In some Asian countries, age might be a positive factor as there is more respect for the experience and knowledge that comes with age. If you don't get a job offer, you can always look into setting yourself up to teach freelance. This way you can focus on the sector that you know well and work with businesses who are in the same line of work as yourself. This would be a selling point in your favour.

I think you need to research the topic extensively and check with the training centre when you sign up for your certificate course. I think that if this is really your vocation, you'll be able to make it work whatever. Just remember that nobody goes into this business to make a fortune.